Bias Layer and Shield Biasing Design

ABSTRACT

A read head is longitudinally biased unidirectionally by laterally abutting soft magnetic layers or multilayers. The soft magnetic layers are themselves magnetically stabilized by layers of antiferromagnetic material that are exchange coupled to them. The same layers of antiferromagnetic materials can be used to stabilize a unidirectional anisotropy of an overhead shield by means of exchange coupling. By including the antiferromagnetic material layer within the patterned biasing structure itself, an additional layer of antiferromagnetic material that normally covers the entire sensor structure is eliminated. The elimination of an entire layer is also advantageous for reducing the inter-sensor spacing in a TDMR (two dimensional magnetic recording) configuration where two sensor are vertically stacked on top of each other.

This is a Divisional application of U.S. patent application Ser. No. 14/848,376 filed on Sep. 9, 2015, which is herein incorporated by reference in its entirety and assigned to a common assignee.

BACKGROUND

1. Technical Field

This disclosure relates generally to thin-film magnetoresistive read sensors and particularly to the use of biasing layers to stabilize magnetic freelayers in configurations that implement “two dimensional magnetic recording”.

2. Description

Magnetic recording heads can bias the reader freelayer by means of the fringe field of the so-called bias layers. This approach is taught by Yanagisawa et al. (U.S. Pat. No. 8,462,467 B2). The bias layer itself is usually a soft magnetic material, and needs to be stabilized by means of magnetic coupling, usually exchange coupling, to another 2^(nd) magnetic layer which is itself stabilized by some means. Usually this 2^(nd) magnetic layer is the upper shield (just above the bias layer) and is itself stabilized by an antiferromagnetic layer such as IrMn, as is taught by Garfunkel et al. (U.S. Pat. No. 8,514,524 B2).

It is instructive to examine the approach of Yanagasawa a bit more closely by examination of an illustration of the structure taught by him in schematic FIG. 1. Referring to schematic FIG. 1, there is shown a longitudinally biased sensor arrangement. The patterned multilayered sensor structure (layers not shown in detail) is labeled 20. An insulating layer, 70, electrically isolates the sensor from symmetrically placed laterally disposed biasing layers, each labeled 60. An upper shield is 50, and a lower shield is 40. The two layers, 60, that are the biasing layer elements, are always soft magnetic films. A stabilizing or unidirectional anisotropy (shown by arrows in 50 and 60) is provided by shield 50 to biasing layers 60 and the shield anisotropy is itself pinned by exchange coupling to the top layer C, labeled 30, which is usually an antiferromagnetic (AFM) layer of IrMn.

Referring next to FIG. 2, there is shown another prior art scheme, this one with multilayer biasing. Note that biasing layer, bracketed as 60, is now formed as a synthetic antiferromagnetic (SyAFM) laminate of two antiferromagnetically coupled layers 62 and 66, (their oppositely directed magnetic anisotropies shown as arrows), separated by an exchange coupling layer 64. But the biasing layers are always soft magnetic material which may be coupled by an exchange coupling layer typically Ru, at positions 64 and 80. The exchange coupling layer 80 provides a coupling to upper shield 50. Whether a single soft magnetic layer is used for biasing as in FIG. 1, or a coupled lamination as in FIG. 2, unidirectional stabilization is ultimately provided by AFM layer 30, also labeled C.

Schemes such as this may work well when there are no geometry constraints and there is room for the antiferromagnetic film, C. However, for so called Two Dimensional Magnetic Recording (TDMR) designs, which employ two sensor structures formed one over the other, Garfunkel et al. (U.S. Pat. No. 8,824,106 B1) have shown that it is critical to minimize the film thicknesses and, correspondingly, the distance between the lower and upper sensors. There is a need to reduce this sensor-to-sensor distance while also providing improvements to the biasing.

SUMMARY

The object of this disclosure is to provide a read sensor that includes at least one sensor element and that is longitudinally biased to have a unidirectional magnetic anisotropy and stabilized using an intrinsic antiferromagnetic layer that allows removal of an antiferromagnetic layer previously used for stabilization.

Referring to schematic FIG. 3, there is shown a freelayer biasing scheme that supports the object described above. The structure in FIG. 3, resembles that of FIG. 1, except that a stabilizing unidirectional anisotropy is provided the sensor, 20, as a result of inserting an antiferromagnetic film, 90, above biasing layer, 61. Layer 90 is an antiferromagnetic film such as IrMn, and in one aspect of the disclosure, layer 90 exchange couples to 61, the sensor magnetic biasing layer below 90 and to layer 50, the upper shield layer above 90. As with other stabilizing antiferromagnetic films, the anisotropy direction is set by an anneal step.

Layer 90, therefore, serves two functions; it stabilizes both the biasing layer, 61, and also the upper shield, 50. It can be used in place of the antiferromagnetic film C, (30, of FIG. 1 and FIG. 2), which stabilized the upper shield layer 50, thus eliminating layer C from the structure of FIG. 3, and in TDMR cases (see FIG. 4, below) thus reducing the sensor to sensor vertical spacing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an ABS view of a prior art biased and stabilized sensor.

FIG. 2 is a schematic representation of an ABS view of an alternate prior art biased and stabilized sensor differing from FIG. 1 in that the biasing structure is a layered configuration.

FIG. 3 is a schematic representation of a biased and stabilized sensor that satisfies the object of this disclosure.

FIG. 4 is a schematic representation of a TDMR (two dimensional magnetic recording) sensor showing how the present structure, when vertically stacked, leads to a smaller separation between top and bottom sensors.

FIG. 5 shows the structure of FIG. 4 with the soft magnetic biasing layer formed as a synthetic antiferromagnetic laminate (SyAFM).

DETAILED DESCRIPTION

Referring again to schematic FIG. 3, there is shown a stabilizing unidirectional magnetic anisotropy provided by insertion of layer 90, adjacent to and on top of the soft magnetic bias layer 61, which are typically layers of NiFe or CoFe formed to a thickness between approximately 40 and 125 Angstroms. Layer 90 is here a patterned AFM layer, formed into a pair of layers, longitudinally disposed and symmetrically placed on each side of the sensor, 20, over the biasing layers 61. Layer 90 is formed to a thickness of between approximately 50 and 200 Angstroms of intrinsically antiferromagnetic material, such as a layer of IrMn.

Subsequent to an annealing process, such as a 2 hour anneal at between 200-250 deg. C in a saturating field, each of this pair of antiferromagnetic layers 90 will exchange couple to the soft magnetic biasing layers, 61, below it to promote and stabilize unidirectional magnetic anisotropy in those layers. It should be noted that the biasing layers 61 require a large net moment in order to bias the sensor. For this reason, forming the biasing layers as synthetic antiferromagnetic structures (i.e., coupling them with opposite moments across a layer of Ru as in FIG. 2) is not preferred, although two soft layers with different thicknesses can be coupled to provide a net moment.

In addition to stabilizing the biasing layers, the pair of patterned antiferromagnetic films, 90, will be exchange coupled to the top shield, 50, thereby providing the shield with a stable unidirectional magnetic anisotropy as well. Thus, layer 90 serves two functions; it stabilizes both the pair of bias layers, 61, and also the top shield 50. It can be used in place of the antiferromagnetic film C, 30, in prior art FIG. 2 thus completely eliminating that film, and in TDMR structures thus reducing the top sensor to bottom sensor vertical spacing. It is a further aspect of the process that the antiferromagnetic films can also be sandwiched between pairs of soft magnetic biasing layers if the biasing configuration, 61, is formed as a multilayered structure rather than a single layer.

Referring finally to FIG. 4, there is shown schematically a two dimensional magnetic recording (TDMR) vertically stacked double sensor structure (top sensor 20, bottom sensor 25), having a reduced sensor-to-sensor spacing (shown by the double arrow between sensor freelayers 10 and 15) because an extra exchange coupling AFM layer, that would typically be formed on top of the top shield 50 of the bottom sensor 25, has been eliminated. This eliminated layer of AFM material is shown as layer 30 (or C) in FIG. 2. In FIG. 4, the effect of this layer is replaced by the laterally disposed symmetric pair, 90, which does double-duty of stabilizing both the soft bias layers 61 and the bottom sensor top shield 50.

As FIG. 4 illustrates, the separation between the bottom sensor and the top sensor is now a result only of the combined thicknesses of the bottom sensor top shield, 50, a non-magnetic spacer layer, 55, and the top sensor bottom shield 45. A blanket covering antiferromagnetic layer (layer 30 of FIG. 2) that would have been used to cover the top surface of the bottom sensor top shield 50 to stabilize its unidirectional anisotropy has been completely eliminated. The stabilization is now provided by layer 90, which is an antiferromagnetic layer of a material such as IrMn and which, as in FIG. 3, stabilizes the biasing layer 61 and the top shield 50. Note that we also show the presence of the AFM stabilizing layers, 80, in the top sensor, 20, but they do not contribute to the reduced inter-sensor distance although they will stabilize the top shield, 40, of the top sensor. Finally, as shown in FIG. 5, the soft magnetic biasing layer (layer 61 in FIG. 4) may alternatively be formed as a synthetic antiferromagnetic (SyAFM) laminate (as shown as layer 60 in FIG. 2) of two antiferromagnetically coupled layers, shown as 62 and 66, separated by an exchange coupling layer 64, where the two layers 62 and 66 have different thicknesses to produce a net magnetic moment.

As is understood by a person skilled in the art, the present description is illustrative of the present disclosure rather than limiting of the present disclosure. Revisions and modifications may be made to methods, materials, structures and dimensions employed in forming and providing a single or multiple sensor read head with longitudinally disposed patterned antiferromagnetic stabilized biasing layers, while still forming and providing such a structure and its method of formation in accord with the spirit and scope of the present disclosure as defined by the appended claims. 

What is claimed is:
 1. A read head having a longitudinally biased freelayer with unidirectional anisotropy in said longitudinal direction, comprising: a top shield; a bottom shield a patterned sensor placed between said top and bottom shields wherein said patterned sensor includes said freelayer having a unidirectional magnetic anisotropy aligned in a horizontal direction; a layer of dielectric material contiguous with lateral patterned sides of said sensor; a pair of soft magnetic films or a pair of multilayers of soft magnetic films symmetrically abutting said layer of dielectric material and biasing said freelayer along said direction of unidirectional magnetic anisotropy; a pair of antiferromagnetic layers exchange coupled to said soft magnetic biasing layers or said multilayer of soft magnetic biasing layers and, thereby, stabilizing said biasing of said freelayer; wherein said top shield is also biased in the same direction as said freelayer and wherein said top shield is exchange coupled to said pair of antiferromagnetic layers and is also provided with a unidirectional magnetic anisotropy and stabilized thereby.
 2. The read head of claim 1 wherein each of said pair of antiferromagnetic layers is formed on top of said soft magnetic biasing layers or said multilayer formation of soft magnetic biasing layers.
 3. The read head of claim 1 wherein each of said pair of antiferromagnetic layers is sandwiched between a pair of soft magnetic biasing layers and thereby directly couples to each of said soft magnetic biasing layers that reside above and below said sandwiched antiferromagnetic layer.
 4. The read head of claim 2 wherein each of said pair of antiferromagnetic layers formed on the top of said soft magnetic biasing layers or on the top of said multilayered formation is exchange coupled to said top shield layer and thereby provides a unidirectional magnetic anisotropy to said top shield layer as well as said biasing layers.
 5. The read head of claim 3 wherein each of said pair of antiferromagnetic layers sandwiched between and directly coupled to each of a pair of soft magnetic biasing layers is also exchange coupled to said top shield layer thereby providing a unidirectional magnetic anisotropy to said top shield layer as well as said pair of soft magnetic biasing layers.
 6. The read head of claim 1 wherein said soft magnetic biasing layer is a multilayer of soft magnetic layers and wherein adjacent pairs of soft magnetic layers may be antiferromagnetically coupled, while possessing a net magnetic moment by virtue of having different thicknesses, by means of an intermediate antiferromagnetically coupling layer.
 7. The read head of claim 6 wherein either or both individual layers of antiferromagnetically coupled adjacent pairs of soft magnetic layers may be exchange coupled to an antiferromagnetic layer.
 8. The read head of claim 1 wherein said soft magnetic biasing layer or multilayers may be formed of the soft magnetic alloys NiFe, CoFe, FeCo, Fe or their combinations.
 9. The read head of claim 6 wherein said layer of antiferromagnetically coupling material is a layer of Ru and wherein said antiferromagnetic coupling is a negative exchange coupling.
 10. The read head of claim 1 wherein said exchange coupling produces said unidirectional anisotropy as a result of an annealing process carried out at a temperature of between 200-250 deg. C., for a period of approximately 2 hours in a saturating magnetic field. 